On the other hand, the Nuclear and Industrial Safety Agency, who was skeptical of criticality yesterday, now says, "We cannot rule out the possibility of localized criticality."

OK it's a "good cop, bad cop" routine, or a "covering all the bases" approach. If both "spontaneous fission" and "criticality" are mentioned in the same news, the Japanese government/TEPCO can say "See, we told you, either way."

Regarding the radioactive xenon detected from the gas inside Reactor 2 of Fukushima I Nuclear Power Plant, TEPCO revealed that the analysis of the amount of xenon detected led the company to conclude that it was a natural fission of a radioactive material, not criticality where nuclear fission takes place continuously.

The gas from inside the Containment Vessel of Reactor 2 was sampled and analyzed on November 1 and 2. A minute amount of xenon-135 was detected, and TEPCO said it was possible that there had been a recent nuclear fission, and that the localized criticality took place temporarily.

Since curium-242 and curium-244, the radioactive materials which exist in nuclear fuel, undergo natural fission and generate xenon, TEPCO calculated the density of xenon based on the amount of these nuclides. The calculation mostly matched the density detected from the samples.

According to TEPCO, the density of xenon would be much greater if there was a criticality. Xenon this time therefore is from spontaneous fission, not from criticality, says TEPCO. "Spontaneous fission" is a phenomenon in which radioactive materials other than uranium fissions naturally, and it does not cause criticality. TEPCO says it will submit the report of the findings to the Nuclear and Industrial Safety Agency under the Ministry of Economy, Trade and Industry, who will evaluate whether the conclusion is appropriate.

The NISA spokesman Yoshinori Moriyama says about TEPCO's analysis, "We think it is highly possible that it is a spontaneous fission, but we cannot rule out completely the possibility of localized criticality. We would like to evaluate TEPCO's analysis as well as analysis by experts. We will assess various risks and make sure TEPCO has emergency measures ready, including injecting water with boric acid."

Uh... what about krypton-85? Is this produced in spontaneous fission of curium? If it is spontaneous fission, why was not happening on October 28?

Could be a publicity stunt - crying wolf and acting concerned for the sake of media attention. And behold, a quick sigh of relief the next day. Catch and release. Also, when a real criticality happens it won't be such breaking news any more. Win-win for Tepco.

"If it is spontaneous fission, why was not happening on October 28?" - The first analysis was on November 1.

"why was not happening on October 28?" Tepco did not say that it was not happening. Tepco used a measurement method with a very high detection limit on October 28, so that the amounts of Xe, if there were any, could not be detected. On November 1 and November 2, the detection limit was lowered and only then could the small quantity of Xenon be detected. See "Detection limits" in http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111102_04-e.pdf

About my coverage of Japan Earthquake of March 11

I am Japanese, and I not only read Japanese news sources for information on earthquake and the Fukushima Nuke Plant but also watch press conferences via the Internet when I can and summarize my findings, adding my observations.

About This Site

Well, this was, until March 11, 2011. Now it is taken over by the events in Japan, first earthquake and tsunami but quickly by the nuke reactor accident. It continues to be a one-person (me) blog, and I haven't even managed to update the sidebars after 5 months... Thanks for coming, spread the word.------------------This is an aggregator site of blogs coming out of SKF (double-short financials ETF) message board at Yahoo.

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